A: Leaves turn beautiful colors each autumn as they lose their pigment, die, and fall off the tree. As we age, our "leaves" turn gray or white as the hair's pigment cells, which give hair its color, die.

This loss of pigment, or melanin, is due mainly to the natural aging process and genetics, but also due to things we do to our body.

For example, have you ever noticed that some longtime smokers look older, grayer, and more wrinkled than they should for their age? A 1996 research study published in the British Medical Journal looked at 152 men and 152 women younger than 50 who smoked. They observed that 14 men and 67 women developed gray hair before the age of 50, compared with just 7 men and 27 women of the same ages who were nonsmokers.

While they were unable to explain the association between smoking and grayness, they speculated that smoking may somehow accelerate the biological clock. Alcoholism and poor nutrition are two other factors that may affect hair.

Wrinkles (sun damage excluded), gray or white hair, and hair loss are just a few of the age-related changes programmed into each of us. As we unravel the mysteries of our DNA, we may one day gain the ability to repair defective or damaged genetic information. While reversing gray hair seems trivial when compared with other more serious health concerns, the aging process is linked to serious diseases such as Alzheimer's.

The time in your life when gray or white hair will appear is largely inherited, so if either of your parents or older siblings develop premature grayness, so too may you. For many folks like me, any color is better than no hair at all.

Mitchell Hecht specializes in internal medicine. Send questions to him at: "Ask Dr. H," Box 767787, Atlanta, Ga. 30076. Due to the large volume of mail received, personal replies are not possible.